Lecture 8: Object Oriented Design: Inheritance

lecture video

Textbook section

2.1-2.2

Object oriented design principles

1. Abstraction
   • give an interface of an abstract data type (ADT)
   • a class implements the interface
2. Encapsulation
   • do not reveal the implementation details; just maintain the interface
3. Modularity
   • organize different components of a system into separate functional units

Inheritance

• hierarchical; uses “is-a” relationships
• we say that a subclass or child class extends a base class, parent class, or super class
• child class can augment by adding new fields and methods
• can also override an existing method
• use super keyword to refer to parent class
• constructors are not inherited

Files used in class

• CreditCard.java
• CreditCardDemo.java
• PredatoryCreditCard.java

Additional exercises

• Create another class, AirlineCreditCard, that inherits from the CreditCard class. It should have the additional private fields airline (String type) and miles (double type). It should have a constructor that calls the CreditCard constructor using the super keyword and sets the values of the two new fields. It should override the charge method to also add one mile per dollar spent to the miles total. (Try to use the super keyword again to call the charge method from the parent class.) Add a getMiles() method and write some code in CreditCardDemo.java to test that your new class is working.